Amplifier



Aug. 29, 1933- v. M. COUSINS AMPLIFIER Filed Sept. 30, 1932 //v VENTOR V. M. COUS/NS im 3W ATTORNEY laienied Au AMPLIFIER Van Cousins, Lyndhurst, N. J., assignor to l'" o i elephone Laboratories, incorporate N. Y., a Corporation of New. Yin.

application September 30, 1932 Serial No. 635A??? 6 Claims.

This inven on relates to amplifiers using space discharge devices and more especially to amplifiers in which t" e devices are arranged in pushpull or balanced relation.

In amplifiers using space discharge devices including g cathode and anode, the grid bias is often obtained from an impedance inserted in the anode circuit of the device. lvlchlally Patent 1,848,137, March 8, 1932, shows how dependent resistors in the anode on .its improve the operation and balance 0. uch circuits when applied to devices arranged in puslnpull or al anced relation.

The present invention has as an object the improvement of the operation amplifiers involving circuits of type noted.

More specifically it is an object of this tion to improve the response of balanced fiers at low frequencies.

Another object is to control the regenerative eilects of even order products of modulation or parallel sin g to the point of practical elimination, in ampllners or the balanced type.

'A feature of the invention is a single capacity connected between the cathodes of the space discharge devices or a balanced amplifier in shunt to the resistors.

Another feature of the invention is a filter comprisi a resistance and capacity, for each invenampli- W1 "re ay the regenerative effects of even pro of modulation nay be reduced or s imina ed from the circuits of the space devices connected in balanced relation.

It is desired to point out that whereas the description which follows is written t i the standpoint of degeneration of second order products of modula ion by a proper choice or the resistance and capacity ing up the so-called filter, a phase s t or" t e feedback voltage may be obtained which produce positive regeneration at low frequencies.

The inventio toge" r with additional objects and features, wil oe un rstood from the following descri and attached drawing forming a part is diagrammatic slzetch of a pref oi i" l Referring :c lug. input tran foriner 2 h ry winding 1 and a sec ing two parts 8 3' nets of the secthe grids l and 5 and 7.

ondary winding of space discharge The primary winding 1 of transformer 2 may be connected to any source, the output of which to the cathodes or filaments irom respective secondary windings 12, 13 of filament heating transformers. It is to he understood, however, that the invention is applicable to devices with direct current heating source or to the heater type device which has gone into considerable use. The primary winding of the cathode heating transformer has not been shown as the arrangement is believed well known.

Anode current is obtained from source 15, illustrated as a battery, but this source may be any direct current source such as rectified alternatin'g current;

The individual biasing resistors are shown at 16 and 17 shunted by condenser 18.

Associated with biasing resistors and 17 are filters comprising resistances 20, 21 and condensers 22 and The common ground point of the input circuit is at 19.

An, output transformer 24 having a divided primary winding is connected in the well known manner to the anodes 10 and 11, and its midpoint connected to source 15. The secondary winding of transformer as may be connected to any utilization circuit.

The input circuits or the amplifier may be traced from ground 19, resistances as or 21, secondary windings 3 or 3', or 5, cathodes 8 or 9, grid bias resistors 16 or 17 to ground 19.

The anode circuits be traced from grounded source 15, inid-point of primary winding of transformer 21 through each half of this winding to t e anodes and i1, cathodes 8 and 9, resistors 16 and 17 to ground at 19. The IR drop of the anode current through resistors 1-5 and 17 provides the bias for the grids 4 and E- in a well known manner.

It will be noted that the bias resistors are common to the grid and anode circuits of each of the devices 6 and 7. They are also common to the input and output circ "s of the amplifier considered as a unit. Now since the signal voltage in the anode circuit is in phase opposition to the signal voltage in the grid circuit unless some means were provided to suppress in the grid circuits the signal voltages derived from the anode circuits due to the drop of potential across the resistors 16 and 17, there would be a reduction in the amplifier gain. Condenser l8 oiiers a path of low impedance at the signal frequency across the two bias resistors 16 and 17 in series and thus effectively prevents voltages of the signal or other desired frequencies from being impressed on the grids from across these bias resistors. The individual grid filter condensers 22, 23 tend to suppress signal frequencies from the grid circuits but their action is supplemented by condenser 18 which directly shunts the bias resistors together with the grid filters.

As is well known in circuits of the type herein described second order products of modulation occur in the individual circuits of the space discharge devices but not in the circuit of the amplifier as a Whole. To reduce or substantially eliminate the degenerative effects of these second order products, the filter consisting of resistance and capacity 22 in the one case and resistance 21 and capacity 23 in the second case are provided, the capacities and resistances are chosen of such value that the degenerative effects of the even order products may be practically completely eliminated and hence do not interfere with the proper amplification of the desired frequencies.

It is found that by controlling the capacities 22, 23 and 18 in relation to the resistances 20 and 21, a change in phase of the signal frequencies, as ecially the lower frequencies, can be affected so as to modify the action and in some cases actually cause an aiding feedback so as to increase amplification. With condenser 18 absent this effect is also obtainable by varying capacities 22, 23 in relation to resistances 20 and 21.

It is to be understood that whereas the invention has been described in connection with but one embodiment, it is to be limited only by the scope of the appended claims.

What is claimed is:

1. An amplifier comprising space discharge devices arranged in push-pull relation, individual grid bias resistors in the anode circuits of said devices and a two-terminal impedance connected between the cathodes of said devices short circuiting said resistors for alternating current of the frequency to be amplified.

2. In an amplifier, space discharge devices arranged in balanced relation and a condenser conecting the cathodes of said devices of such capacity as to be of negligible impedance to alternating currents of the frequency to be amplified.

3. In an amplifier, space discharge devices arranged in balanced relation, a common source of anode current, individual grid bias resistors in the anode circuits connecting the cathodes of the devices to the negative terminal of the anode current source and to the grids of the devices and a condenser of small impedance to alternating currents of the frequency to be amplified,

as compared to that of said resistors, in shunt to 5. An amplifier comprising space discharge de- 4 vices arranged in push-pull relation, individual grid bias resistors in the anode circuits of said devices, unitary means short circuiting said resistors for alternating currents of the frequency to be amplified, and individual resistance capacity filters comprised in part of said resistors for preventing application to the grids of undesired frequency components.

6. In a push-pull amplifier comprising a pair of space discharge devices each having a cathode, an anode and a grid or control element, individual grid-to-cathode circuits, each including a grid bias resistor, a connection from said resistors to the negative pole of the plate potential source, a connection from each resistor to its corresponding grid, means including an individual condenser shunting each of said resistors, and a condenser connected directly between the cathodes, each of said condensers offering negligibly low impedance to currents of the frequency to be amplified.

VAN M. COUSINS. 

